CONTAMINATION FEASIBILITY STUDY Stakeholder Meeting Wednesday, - - PowerPoint PPT Presentation

THOMPSON LAKE PAH CONTAMINATION FEASIBILITY STUDY

Stakeholder Meeting Wednesday, October 30, 1:00 pm

Item XI. LMRWMO Meeting 11-13-13

PRESENTATION OVERVIEW

1.

Project Overview/Project History

2.

PAH Contamination

3.

Current Project Goals

4.

Initial List of Alternatives / Pros & Cons – STAKEHOLDER INPUT NEEDED

5.

Regulatory Issues – STAKEHOLDER INPUT NEEDED

6.

Other Questions / Suggestions / Concerns / Next Steps

Location Map and Drainage Area

Lake Inlet and Area of Concern

Inlet Area (Potential Sediment Forebay Area) Main Inlet

Lake Inlet and Area of Concern

Inlet Area (Potential Sediment Forebay Area) Sediment Plume Main Inlet

Lake Inlet and Area of Concern

Inlet Area (Potential Sediment Forebay Area) Contamination Extents – Initial Testing Main Inlet

Additional Sampling

Further testing indicated that PAH contamination is present throughout the lake

PAHs – Description

• What are PAHs?
• Polycyclic Aromatic Hydrocarbons – specific group of over 100

chemicals, natural and man-made

• Most bound to sediment
• Products of incomplete combustion (fossil fuels, forest fires, coal

tar, etc.) – very common in nature and in urban environments

• Coal tar based sealant identified as a major contributor (already

banned in West St. Paul; banned statewide as of Jan. 1, 2014)

• Primary Concerns
• Ecological health risks – bottom-dwelling organisms, others
• Human health risks - many are known or probable carcinogens
• PAHs accumulate in water bodies (sediment)
• Dredged PAH-contaminated sediment considered a health risk
• Two categories of PAH concern:

1.

PAHs in sediment dredged out of water body (more exposure)

2.

PAHs in sediment that stays in water body (less exposure)

PAHs – Concerns

PAHs: Stormwater Pond Vs. Lake

• Stormwater Treatment Ponds
• Stormwater treatment requires a certain amount of storage volume
• Many ponds have reached their design life and require

maintenance dredging

• PAH contamination showing up at high concentrations - in many

ponds at levels requiring landfilling of dredged material (high cost)

PAHs: Stormwater Pond Vs. Lake

• Lakes and Wetlands
• Natural water bodies – not designed “stormwater ponds”
• Not the same impetus (storage volume) for maintenance
• Many act as a “treatment” areas for stormwater runoff
• Retrofitting a treatment “forebay” provides a defined area for

sediment accumulation

Current Project Goals

• Improve Problem

Definition

• Review Latest PAH

Research

• Evaluate All

Management Options

• Address Stakeholder

Goals / Concerns

Initial List of Alternatives / Pros & Cons

1) No-Action Alternative 2) Construct Settling Basin and Dredge Sediment Plume –

Disposal in Landfill

3) Construct Settling Basin and Dredge Limited Area –

Disposal in Landfill

4) Construction of Settling Basin Only 5) Alternative: Nearby Disposal Site – MPCA Pilot Project 6) Alternative: In-Situ Treatment Pilot Project – Methods

Under Consideration

STAKEHOLDER INPUT NEEDED

• 1. No-Action Alternative
• Leave as-is; no excavation or construction
• May include continued studies/monitoring
• Pros
• No immediate costs for construction or excavation
• Maintains status quo – low risk of making things drastically worse
• May be able to take advantage of future technical or regulatory

developments

• Cons
• Does nothing to address ongoing pollution of the Lake
• Pushes the problem into the future
• Largely wastes the effort and funding invested up to this point
• Cost Range: $0 - $50,000 (studies/monitoring)

• 2. Construct Settling Basin and Dredge

Sediment Plume – Disposal in Landfill

• Original proposed alternative
• Full cleanout and construction of sediment pond
• Pros
• Takes contaminated and excess sediment out of Lake
• Landfilling sediment eliminates any further exposure risk
• Provides stormwater treatment at Lake inlet
• Cons
• High cost
• Uncertain level of benefit
• Potential risk of contaminant resuspension during excavation
• Cost Range: $1,000,000 - $1,500,000

• 3. Construct Settling Basin and Dredge

Limited Area – Disposal in Landfill

• Reduced dredging footprint – based on level of

contamination, budgetary limits, or other considerations

• Construct sediment pond at inlet
• Pros
• Removes some sediment from Lake based on specific criteria
• Reduced cost relative to the “full cleanout” option
• Still provides stormwater treatment at Lake inlet
• Cons
• Still involves substantial excavation costs
• Uncertain benefit / contaminant resuspension concerns remain
• Cost Range: $500,000 - $1,000,000 depending on

specifics

• 4. Construct Settling Basin Only
• Construct proposed sediment pond/forebay at Lake inlet

(storm sewer outfall)

• Highly contaminated sediments would be landfilled
• Do not excavate or do other work in main body of Lake
• Pros
• Provides stormwater treatment at Lake inlet
• Eliminates costs of dredging within main body of Lake
• Reduces or eliminates concerns about contaminant resuspension
• Cons
• Does not immediately address concerns in main body of Lake
• Cost Range: $300,000 - $500,000

• 5. Alternative: Nearby Disposal Site – MPCA

Pilot Project

• Place sediment nearby and cap (per MPCA guidance)
• Disposal alternative for any of the listed options
• Pros
• Eliminates need for landfilling, drastically reducing disposal costs
• Adds to knowledge base regarding sediment management options
• Cons
• Land required nearby; PAHs are present (but not exposed)
• Consumes / modifies landscape area
• Cost Range: Can reduce project cost by 50% or more

• 6. Alternative: In-Situ Treatment Pilot Project
• In-situ remediation pilot project in main body of Lake (along

with forebay construction)

• Pacific Northwest National Laboratory has done similar

research in saline environment; interested in participating

• Phytoremediation and bioaugmentation
• Pros
• Stormwater treatment at Lake inlet would still be provided
• Could result in reduction of PAH concentrations in sediment
• Adds to knowledge base regarding PAH remediation
• Cons
• Pilot project is experimental; may not achieve desired results
• Cost Range: Adds cost of pilot project ($50,000 - $150,000)

• MnDNR – Public Waters Work Permit, Other

Requirements

• MPCA – Construction Permit, Endorsement/Assistance for

Pilot Project

• Dakota County – Approval for Pilot Project (Alternative

Disposal Site)

• Other Stakeholder Requirements / Restrictions

Regulatory Issues

STAKEHOLDER INPUT NEEDED

Initial List of Alternatives / Pros & Cons

1) No-Action Alternative 2) Construct Settling Basin and Dredge Sediment Plume –

Disposal in Landfill

3) Construct Settling Basin and Dredge Limited Area –

Disposal in Landfill

4) Construction of Settling Basin Only 5) Alternative: Nearby Disposal Site – MPCA Pilot Project 6) Alternative: In-Situ Treatment Pilot Project – Methods

Under Consideration

STAKEHOLDER INPUT NEEDED

• 6. Other Questions / Suggestions /

Concerns / Next Steps